mark the selected items

app/src/main/java/com/simplemobiletools/gallery/activities/PhotosActivity.java

@@ -26,6 +26,7 @@ import java.util.regex.Pattern;
 public class PhotosActivity extends AppCompatActivity implements AdapterView.OnItemClickListener, GridView.MultiChoiceModeListener {
     private List<String> photos;
     private int selectedItemsCnt;
+    private GridView gridView;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -34,8 +35,8 @@ public class PhotosActivity extends AppCompatActivity implements AdapterView.OnI
 
         photos = new ArrayList<>();
         final String path = getIntent().getStringExtra(Constants.DIRECTORY);
-        final GridView gridView = (GridView) findViewById(R.id.photos_grid);
         final PhotosAdapter adapter = new PhotosAdapter(this, getPhotos(path));
+        gridView = (GridView) findViewById(R.id.photos_grid);
         gridView.setAdapter(adapter);
         gridView.setOnItemClickListener(this);
         gridView.setMultiChoiceModeListener(this);
@@ -45,6 +46,7 @@ public class PhotosActivity extends AppCompatActivity implements AdapterView.OnI
     }
 
     private List<String> getPhotos(final String path) {
+        photos.clear();
         final Uri uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
         final String where = MediaStore.Images.Media.DATA + " like ? ";
         final String[] args = new String[]{path + "%"};

app/src/main/java/com/simplemobiletools/gallery/adapters/PhotosAdapter.java

@@ -8,11 +8,10 @@ import android.widget.BaseAdapter;
 import android.widget.ImageView;
 
 import com.bumptech.glide.Glide;
+import com.simplemobiletools.gallery.R;
 
 import java.util.List;
 
-import com.simplemobiletools.gallery.R;
-
 public class PhotosAdapter extends BaseAdapter {
     private final Context context;
     private final List<String> photos;
@@ -36,7 +35,7 @@ public class PhotosAdapter extends BaseAdapter {
         }
 
         String path = photos.get(position);
-        Glide.with(context).load(path).centerCrop().crossFade().into(holder.photoThumbnail);
+        Glide.with(context).load(path).placeholder(R.color.tmb_background).centerCrop().crossFade().into(holder.photoThumbnail);
 
         return view;
     }

app/src/main/res/drawable/selected_mask.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@color/activated_item_foreground"/>
+</selector>

app/src/main/res/drawable/selected_pressed_mask.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@color/pressed_item_foreground"/>
+</selector>

app/src/main/res/drawable/selector.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@drawable/selected_pressed_mask" android:state_pressed="true"/>
+    <item android:drawable="@drawable/selected_mask" android:state_activated="true"/>
+</selector>

app/src/main/res/layout/activity_photos.xml

@@ -5,9 +5,9 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@android:color/black"
+    android:choiceMode="multipleChoiceModal"
     android:columnWidth="@dimen/photo_tmb_size"
     android:horizontalSpacing="1dp"
     android:numColumns="auto_fit"
     android:stretchMode="columnWidth"
-    android:choiceMode="multipleChoiceModal"
     android:verticalSpacing="1dp"/>

app/src/main/res/layout/photo_item.xml

@@ -3,7 +3,7 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@color/tmb_background">
+    android:foreground="@drawable/selector">
 
     <com.simplemobiletools.gallery.MyImageView
         android:id="@+id/photo_thumbnail"

app/src/main/res/values/colors.xml

@@ -5,4 +5,6 @@
     <color name="colorAccent">#FF4081</color>
     <color name="tmb_background">#ff222222</color>
     <color name="actionbar_grey">#66000000</color>
+    <color name="pressed_item_foreground">#11000000</color>
+    <color name="activated_item_foreground">#44000000</color>
 </resources>